Classification of Joints Used in Steerable Instruments for Minimally Invasive Surgery1

Tips of steerable minimally invasive surgical (MIS) instruments come in numerous configurations when it comes to the joints used for enabling and transferring rotational motion. Even though previous reviews of steerable MIS instruments were carried out, they focus mainly on actuation, Catherine et al. [1]; control principles, Fan et al. [2]; or robotics and MEMS, Cepolina and Michelini [3]. Therefore, the primary objective of this literature review is to provide a comprehensive overview and clear classification of steerable MIS instruments with respect to the fundamental mechanical design and working principles of their tip articulations. Such a classification would serve to better understand the essence of the state-of-the-art steerable constructions, thereby helping to establish a set of design guidelines for the next generations of steerable minimally invasive surgical instruments.For simplicity and clear focus of this review, the literature search is based purely on mechanical steerable constructions, excluding pneumatics, hydraulics, electronics, magnetics, or shape memory alloy solutions. While considering the scientific literature it was recognized that the covered scope of the fundamental articulation principles was insufficient for this overview. Hence, for the sake of creativity and broadness of this overview, the classification is not limited to the existing steerable MIS instruments or scientific papers; however, it reviews the entire Espacenet patent database.The following keywords were used to perform the patent search: endo* or lapar* or surg* in title and steer* or articu* or deflect* in title or abstract. Due to the extensiveness of this search query, the results were cropped down to include World (WO), U.S. and European (EP) patents only. In particular, the patents shown in this classification were further limited to the period of the last decade, 2003–2013, with a few exceptions that predated this period, yet helped to fill the missing gaps in the classification.For coherence, the 840 reviewed patents, categorized by the instrument tip's joint type, were further reduced to the most recent up-to-date patents (valid as of Oct. 31, 2013) by a given patent assignee.Besides investigating the existing inventions, new joint type was determined using the abstracting, categorizing, reflecting, reformulating, and extending (ACRREx) method [4].The patent search results revealed the use of two basic joint types—planar (2D) and spatial (3D). Both joint types are further split into more subcategories depending on the means of establishing the joint articulation, as outlined later. Figure 1 presents a graphical summary of the joint type classification, listing all the relevant up-to-date patents for each joint type.The working principle of a planar joint is two dimensional and allows for one rotational degree of freedom (DOF), whereas a spatial joint is simply a geometrical extension of the planar joint allowing for more DOF. The spatial joint category comprises a perpendicular mirrored and a revolved configuration. In comparison with the planar joint, the perpendicular mirrored configuration uses an additional plane of motion placed orthogonally to the first one in order to increase the number of DOF to two—providing 3D motion. Similarly to the perpendicular mirrored joint, the revolved joint is a modification of the planar joint. Here, the planar joint, or its 2D cross section, is revolved around its vertical central axis, hence transforming it into a spatial joint. Such a revolved joint allows not only for sideways rotation in two perpendicular planes but also for rotation along its vertical axis, thus featuring all three rotational DOF in a single joint. Certain planar joint configurations, i.e., rolling belted joint and sliding hinged joint, cannot be revolved into a spatial three-DOF joint, either due to the theoretical infeasibility or the elimination of DOF due to such a construction.The rotational motion of all of these joints is established by either rolling, sliding, the combination of rolling and sliding, or bending. The rolling and sliding categories are further split to more subcategories based on the phenomenon or feature used for transferring the rotational motion, i.e., friction, teeth, belts, curved features, and hinges.In general, the most listed joint types were identified as the sliding curved joints (DEAM's Miflex, Tuebingen's Radius Surgical System, Novare's RealHand, Covidien's SILS Hand), the sliding hinged joints, and the bending joint category overall (CambridgeEndo's Laparo-Angle). The ACRREx method helped identify a novel joint type as a revolved rolling toothed joint. Yet, it was recognized that no single fundamental joint type can be considered as ideal and that novel and preferably more superior joint configurations can be generated by combining several fundamental categories together.The research of Filip Jelínek was performed within the framework of CTMM, the Center for Translational Molecular Medicine, Project MUSIS (grant 03O-202). The research of Ewout A. Arkenbout and Paul W. J. Henselmans was supported by Technology Foundation STW.